Cobalt base alloy



July 19, 1955 G. T. HARRIS ET AL COBALT BASE ALLOY Filed Oct. 3l, 1950 ma uw lo /J o L 8 M .b 55g/ w ,7 M //f/ a@ @m s am w. wf am ..05

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Carbide Formers (V+ Mo+Nb) Per Cem.

INVENToRs. GE OF F RE ,V THOMAS HA RR/S HENg CA VE CH/LD ATTORNEYS.

United States Patent O COBALT BASE ALLOY Geoffrey Thomas Harris and Henry Cave Child, Sheffield, England, assignors to William Jessop & Sons Limited, Shetlield, England, a British company Application October 31, 1950, Serial No. 193,238

1 Claim. (Cl. 75-171) This invention relates to cobalt base alloys and has for its object the provision of alloys from which castings may be made having good strength (particularly creep strength) and resistance to oxidation at elevated temperatures, for example, 750 C.

According to this invention alloys contain:

Carbon above 1% to 2.96%; silicon .35 to 1.07%; manganese .54 to 1.06%,l nickel 7.8 to 12%; cobalt 35 to 57%; chromium 17.6% to 19%; boron 0 to 0.5%; and carbide-forming elements consisting of molybdenum 2.9% to 5.4%, vanadium 2.4% to 8.2%, and niobium 1.9% to 4.8%, and the remainder iron with unavoidable impurities.

Since tantalum is usually present with commercial niobium, the reference to niobium in this specification includes, besides the pure product, such amounts of tantalum as are usually present in commercial niobium, such, for example, as ferro-niobium.

Increasing the carbon within the range mentioned and using proportionately higher totals of the carbide forming elements (vanadium, molybdenum, niobium etc.) has the effects of increasing the creep strength but the cold ductility decreases. The amounts of carbon and carbide formcrs are therefore selected according to which of these properties is required to predominate or to the required degree of balance between the two.

For optimum results it is desirable to maintain a balance between carbon and the carbide formers, vanadium, tungsten, moylbdenum, niobium, titanium and tantalum. For carbon of 1.01% the total of the carbide formers should be about 6.7% and for carbon of 3% the total of the carbide formers should be about 16%. Between the limits of carbon indicated proportionate quantities of carbide formers to those given should be employed.

The iron content is preferably as low as is consistent with economy and with the use of ferro-alloys for melt- I,

ln addition Vto yhaving high creep strength the alloys according Vto this invention possess exceedingly high fatigue properties at elevated temperatures. YFor instance, alloy L. 457 has a fatigue strength of i12 tons/ sq. in. at 850 C. for one hundred million cycles.

Where a cold ductility of the order of 1% is deemed satisfactory alloys with a specification of:

Per Cent 2.2 0.8 0.5

are considered to be the most satisfactory. At 750 C. cast material of the above composition will sustain stresses of 22 tons/ sq. in. and 17 tons/sq. in. for 100 and 1000 hours respectively, the minimum creep rate being 2.0 104 and 1.5 105 per hour respectively.

At 850 C. the material will sustain stresses of 12.5 tons/sq. in, and 8 tons/sq. in. for 100 and 1000 hours respectively, the minimum creep rates being 2 104 and 1.2 l05 per hour respectively. The hot ductility of these castings is approximately 3%.

The illustrative drawing accompanying the specilication shows a graph based on alloys made according to this invention and having as main constituents nickel about 10%, iron about 15%, chromium about 19% the balance being cobalt and usual amounts of silicon and manganese, plus the carbide formers vanadium, molybdenum and niobium in the ratio 1.411207. The graphs were prepared on the mean of two tests on cold sand mould castings and the figures give the time to fracture in hours under a stress of 10 tons per square inch at a temperature of 850 C. The shaded band represents alloys having particularly good properties.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

Metal alloys having high creep strength and consisting of carbon above 1% to 2.96%, silicon .35 to 1.07%, manganese .54 to 1.06%, nickel 7.8 to 12%, cobalt 35 to 57%. chromium 17.6 to 19%, boron Oto 0.5%, and carbide-forming elements consisting of molybdenum 2.9 to 5.4%, vanadium 2.4 to 8.2% and niobium 1.9 to

f d t f 30 4.8%, and the remainder iron with unavoidable impuri- {ng PUYP0S5- AS an mdlcatlon of pre en e amoun S o ties, the total percentage of elements in the carbidenon a range of 10 to 20% may b? {Helmoned' forminfy group being between 6.7 and 16% the propor- Nickel is preferably kept low w1th1n the above range, t but Where castings from the alloys have to be machined tion of the carbide-forming elements to carbon falling apit is then desirable to use a higher proportion of nickel Proxuflately Wlthm the shaded area 0n the dfawmg, that Within the above range not less than 10% '-J 1s, belng substannally as follows: with carbon between The following are examples of alloys made accord- 1 and about t0 Carblde formel's; With ing to this invention and in each example the balance Carbon between 1.5 and 2% about 8 to 12% carbide consists of iron and the usual impurities: formcrs; with carbon between 2 to 2.5% about 10 to Fracture M Ime lIl llllmllm Melt Reference o Mn s1 Ni oo or W M0 v Nb B hourswnh creep Rate Tlllg 0f 10 tons/sq. Per Hour y in.a1;850c.

L 0.8 0.5 12 45 19 2.9 4.5 1.9 270 15x10-4 As Cast L' 1.0 .s2 11.0 40.5 18.3 2.9 5.8 2.9 481 8 1o Do. L' 1. 06 1.07 7.8 34.9 18.8 4.6 8.2 4.8 370 7.2 105 Do. L' 0.8 0.5 57 19 3.0 4.7 2.1 471 2.2 10-5 Do. L 0.85 0.35 9.8 38.1 19.2 3.8 3.4 2.4 2.7 310 1.4 10-4 D0, L. 0.94 0.84 9.7 37.8 17.6 3.4 5.2 2.0 140 1.9 10-4 D()- L 0.8 0.5 9.0 38 19 5.4 5.9 3.3 375 4. 9 105 Do, L' 0.92 0.50 9.9 49.2 17.8 3. 01 3.26 2.96 3.05 253 8.0 104 Do.

14% carbide farmers; with carbon 2.5 to 3% about 12 to 2,309,372 16% carbide formers. 2,513,470 2,537,477 References Cited in the 111e of this patent UNITED STATES PATENTS 42 2,030,343 Wissler Feb. 11, 1936 4463 2,299,871 Baird Oct. 27, 1942 4 Wssler Jan. 26, 1943 Franks July 4, 1950 Mohling Jan. 9, 1951 FOREIGN PATENTS Great Britain Feb. 21, 1935 

